Image-forming optical system, illumination apparatus, and observation apparatus

ABSTRACT

Provided is an image-forming optical system including: a plurality of image-forming lenses that form a final image and at least one intermediate image; and a wavefront disturbing device and a wavefront restoring device that are disposed at positions having any of the intermediate images formed by the plurality of image-forming lenses therebetween and that apply phase modulation to the wavefront of light coming from an object. The wavefront disturbing device and the wavefront restoring device have the same phase distribution including a wave-shaped phase-advancing region and phase-delaying region that are symmetrical to each other, and are paired such that light passes through the corresponding phase-advancing region and phase-delaying region having opposite wave shapes.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation of International Application PCT/JP2014/084493, with an international filing date of Dec. 26, 2014, which is hereby incorporated by reference herein in its entirety. This application claims the benefit of Japanese Patent Application No. 2014-207375, the content of which is incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to an image-forming optical system, an illumination apparatus, and an observation apparatus.

BACKGROUND ART

There is a known method of moving a focal-point position in an optical-axis direction (on the Z axis) by adjusting an optical-path length at an intermediate-image position (for example, see Patent Literature 1).

CITATION LIST Patent Literature

{PTL 1} Publication of Japanese Patent No. 4011704

SUMMARY OF INVENTION

A first aspect of the present invention is an image-forming optical system including: a plurality of image-forming lenses that form a final image and at least one intermediate image; and a first phase modulator and a second phase modulator that are disposed at positions having any of the intermediate images formed by the plurality of image-forming lenses therebetween and that apply phase modulation to the wavefront of light coming from an object. The first phase modulator and the second phase modulator have the same phase distribution including a wave-shaped phase-advancing region and phase-delaying region that are symmetrical to each other, and are paired such that light passes through the corresponding phase-advancing region and phase-delaying region having opposite wave shapes.

A second aspect of the present invention is an illumination apparatus including: any of the above-described image-forming optical systems; and a light source that is disposed on the object side of the image-forming optical system and that generates illumination light to be made to enter the image-forming optical system.

A third aspect of the present invention is an observation apparatus including: any of the above-described image-forming optical systems; and a photo-detector that is disposed on the final-image side of the image-forming optical system and that detects light emitted from an observation object.

A forth aspect of the present invention is an observation apparatus including: any of the above-described image-forming optical systems; a light source that is disposed on the object side of the image-forming optical system and that generates illumination light to be made to enter the image-forming optical system; and a photo-detector that is disposed on the final-image side of the image-forming optical system and that detects light emitted from an observation object.

A fifth aspect of the present invention is an observation apparatus including: the above-described illumination apparatus; and a photo-detector that detects light emitted from an observation object illuminated with the illumination apparatus. The light source is a pulsed-laser light source.

According to this aspect, it is possible to perform multiphoton-excitation observation of the observation object.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic view showing an embodiment of an image-forming optical system used in a microscope apparatus of the present invention.

FIG. 2 is a schematic view showing the image-forming optical system in FIG. 1.

FIG. 3 is an enlarged view of a wavefront disturbing device and a wavefront restoring device in FIG. 2.

FIG. 4 is a schematic view for explaining the operation of the image-forming optical system in FIG. 1.

FIG. 5 is an enlarged view showing portions between an object-side pupil position and a wavefront restoring device in FIG. 2.

FIG. 6 is a schematic view showing an image-forming optical system used in a conventional microscope apparatus.

FIG. 7 is an enlarged view showing an example of a wavefront disturbing device and a wavefront restoring device that constitute an image-forming optical system according to a first modification of an embodiment of the present invention.

FIG. 8 is a diagram showing the positional relationship between the wavefront disturbing device and the wavefront restoring device of the image-forming optical system in FIG. 7.

FIG. 9A is an enlarged view showing an example of the wavefront disturbing device and the wavefront restoring device that constitute the image-forming optical system according to the first modification of an embodiment of the present invention.

FIG. 9B is an enlarged view showing another example of the wavefront disturbing device and the wavefront restoring device that constitute the image-forming optical system according to the first modification of an embodiment of the present invention.

FIG. 9C is an enlarged view showing another example of the wavefront disturbing device and the wavefront restoring device that constitute the image-forming optical system according to the first modification of an embodiment of the present invention.

FIG. 9D is an enlarged view showing another example of the wavefront disturbing device and the wavefront restoring device that constitute the image-forming optical system according to the first modification of an embodiment of the present invention.

FIG. 9E is an enlarged view showing another example of the wavefront disturbing device and the wavefront restoring device that constitute the image-forming optical system according to the first modification of an embodiment of the present invention.

FIG. 10 is a bird's-eye view showing an example of a wavefront disturbing device and a wavefront restoring device that constitute an image-forming optical system according to a second modification of an embodiment of the present invention.

FIG. 11 is a bird's-eye view showing another example of the wavefront disturbing device and the wavefront restoring device that constitute the image-forming optical system according to a second modification of an embodiment of the present invention.

FIG. 12 is a bird's-eye view showing another example of the wavefront disturbing device and the wavefront restoring device that constitute the image-forming optical system according to a second modification of an embodiment of the present invention.

FIG. 13 is an enlarged view showing an example of a wavefront disturbing device and a wavefront restoring device that constitute an image-forming optical system according to a third modification of an embodiment of the present invention.

FIG. 14 is a schematic view showing an observation apparatus according to a first embodiment of the present invention.

FIG. 15 is a schematic view showing an observation apparatus according to a second embodiment of the present invention.

FIG. 16 is a schematic view showing an observation apparatus according to a third embodiment of the present invention.

FIG. 17 is a schematic view showing a modification of the observation apparatus in FIG. 16.

FIG. 18 is a schematic view showing a first modification of the observation apparatus in FIG. 17.

FIG. 19 is a schematic view showing a further modification of the observation apparatus in FIG. 18.

FIG. 20 is a schematic view showing a second modification of the observation apparatus in FIG. 17.

FIG. 21 is a schematic view showing a third modification of the observation apparatus in FIG. 17.

FIG. 22 is a perspective view showing cylindrical lenses as examples of phase modulators used in the image-forming optical system and the observation apparatus in a reference embodiment of the invention, serving as a reference example of the present invention.

FIG. 23 is a schematic view for explaining the effects of employing the cylindrical lenses.

FIG. 24 is a diagram for explaining the relationship between the phase modulation level and the optical power based on the Gaussian optics used for explaining FIG. 23.

FIG. 25 is a perspective view showing binary diffraction gratings as other examples of the phase modulators used in the image-forming optical system and the observation apparatus of the present invention.

FIG. 26 is a perspective view showing one-dimensional sine-wave diffraction gratings as other examples of the phase modulators used in the image-forming optical system and the observation apparatus in a reference embodiment of the invention, serving as a reference example of the present invention.

FIG. 27 is a perspective view showing free-curved surface lenses as other examples of the phase modulators used in the image-forming optical system and the observation apparatus in a reference embodiment of the invention, serving as a reference example of the present invention.

FIG. 28 is a longitudinal sectional view showing conical lenses as other examples of the phase modulators used in the image-forming optical system and the observation apparatus in a reference embodiment of the invention, serving as a reference example of the present invention.

FIG. 29 is a perspective view showing concentric binary diffraction gratings as other examples of the phase modulators used in the image-forming optical system and the observation apparatus in a reference embodiment of the invention, serving as a reference example of the present invention.

FIG. 30 is a schematic view for explaining the effects of a ray traveling along the optical axis when the diffraction gratings are used as the phase modulators.

FIG. 31 is a schematic view for explaining the effects of on-axis rays when the diffraction gratings are used as the phase modulators.

FIG. 32 is a diagram showing details of a center portion for explaining the effects of a diffraction grating that serves as a wavefront disturbing device.

FIG. 33 is a diagram showing the details of the center portion for explaining the effects of a diffraction grating that serves as a wavefront restoring device.

FIG. 34 is a longitudinal sectional view showing spherical aberration devices as other examples of the phase modulators used in the image-forming optical system and the observation apparatus in a reference embodiment of the invention, serving as a reference example of the present invention.

FIG. 35 is a longitudinal sectional view showing irregular-shaped devices as other examples of the phase modulators used in the image-forming optical system and the observation apparatus in a reference embodiment of the invention, serving as a reference example of the present invention.

FIG. 36 is a schematic view showing reflecting-type phase modulators as other examples of the phase modulators used in the image-forming optical system and the observation apparatus of the present invention.

FIG. 37 is a schematic view showing gradient-index devices as other examples of the phase modulators used in the image-forming optical system and the observation apparatus in a reference embodiment of the invention, serving as a reference example of the present invention.

FIG. 38 is a diagram showing an example lens array for the case in which the image-forming optical system of the present invention is applied to a microscope magnification observation apparatus that is used for endoscopy.

FIG. 39 is a diagram showing an example lens array for the case in which the image-forming optical system of the present invention is applied to a microscope provided with an endoscope-type small-diameter objective lens including an inner focusing function.

DESCRIPTION OF EMBODIMENTS

An image-forming optical system 1 according to an embodiment of the present invention will be described below with reference to the drawings.

As shown in FIG. 1, the image-forming optical system 1 according to this embodiment is provided with two image-forming lenses 2 and 3 that are disposed as one set with a space therebetween; a field lens 4 that is disposed at an intermediate-image-forming plane between the image-forming lenses 2 and 3; a wavefront disturbing device (first phase modulator) 5 that is disposed in the vicinity of a pupil position PP_(O) of the image-forming lens 2 at the object O side; and a wavefront restoring device (second phase modulator) 6 that is disposed in the vicinity of a pupil position PP_(T) of the image-forming lens 3 at the image I side. Reference sign 7 in the figure indicates an aperture stop.

As shown in FIG. 2, the wavefront disturbing device 5 and the wavefront restoring device 6 are formed in the same shape. More specifically, as shown in FIG. 3, the wavefront disturbing device 5 and the wavefront restoring device 6 have the same phase distribution including wave-shaped phase-advancing regions (recessed portions) 5 a and 6 a and phase-delaying regions (projecting portions) 5 b and 6 b that are symmetrical to each other. Specifically, in the wavefront disturbing device 5 and the wavefront restoring device 6, the rectangular-wave-shaped phase-advancing regions 5 a and 6 a and phase-delaying regions 5 b and 6 b are formed rotationally symmetrical to each other with respect to an average plane H, and a plurality of pairs of the phase-advancing region 5 a and the phase-delaying region 5 b and a plurality of pairs of the phase-advancing region 6 a and the phase-delaying region 6 b, each pair forming one period, are arranged periodically. In FIG. 3, the wavefront restoring device 6 is reversed and disposed such that the phase-advancing regions 5 a and the phase-delaying regions 5 b of the wavefront disturbing device 5 face the phase-delaying regions 6 b and the phase-advancing regions 6 a of the wavefront restoring device 6. Hereinbelow, the surfaces of the wavefront disturbing device 5 and the wavefront restoring device 6 having the phase-advancing regions 5 a and 6 a and the phase-delaying regions 5 b and 6 b will be referred to as recess-and-projection surfaces, and the planar surfaces on the reverse sides of the recess-and-projection surfaces will be referred to as flat surfaces.

Furthermore, the wavefront disturbing device 5 and the wavefront restoring device 6 are paired such that the light entering from the object O side is transmitted through the wave-shaped phase-advancing regions 5 a and 6 a and the phase-delaying regions 5 b and 6 b that correspond to each other and have opposite wave shapes. Specifically, as shown in FIG. 2, the wavefront disturbing device 5 and the wavefront restoring device 6 are disposed such that their positions are shifted from each other by half a period in the direction perpendicular to the optical axis. By doing so, the light coming from the object O side and transmitted through the phase-advancing regions 5 a of the wavefront disturbing device 5 is transmitted through and exits from the phase-delaying regions 6 b of the wavefront restoring device 6, and the light coming from the object O side and transmitted through the phase-delaying regions 5 b of the wavefront disturbing device 5 is transmitted through and exits from the phase-advancing regions 6 a of the wavefront restoring device 6.

Note that the wavefront disturbing device 5 and the wavefront restoring device 6 may be disposed either such that their recess-and-projection surfaces face the field lens 4, as shown in FIG. 2, or such that their flat surfaces face the field lens 4. Furthermore, the wavefront disturbing device 5 and the wavefront restoring device 6 may be disposed such that their recess-and-projection surfaces face the object O side or, conversely, such that their recess-and-projection surfaces face the image I side. However, of the four types of arrangement method described above, the former two, namely, the arrangement in which both of the recess-and-projection surfaces of the elements face the field lens 4 and the arrangement in which both of the flat surfaces of the elements face the field lens 4, are more preferable than the latter two, from the standpoint of the wave-recovery precision.

The wavefront disturbing device 5 and the wavefront restoring device 6 disposed in this manner can apply mutually complementary phase modulations to the wavefront of the light by means of the surface shape of the optical medium. Specifically, the wavefront disturbing device 5 is configured so as to disturb the wavefront when light that is emitted from an object O and that is focused by the image-forming lens 2 at the object O side passes therethrough. By disturbing the wavefront by means of the wavefront disturbing device 5, an intermediate image formed at the field lens 4 is made unsharp.

On the other hand, the wavefront restoring device 6 is configured so as to apply a phase modulation to the wave of light in such a way that the wavefront disturbance applied by the wavefront disturbing device 5 is cancelled out when light focused by the field lens 4 passes therethrough. The wavefront restoring device 6 possesses opposite phase properties relative to those of the wavefront disturbing device 5, so that a sharp final image I is formed by canceling out the wavefront disturbance.

More general concepts related to the image-forming optical system 1 according to this embodiment will now be described in detail.

In the example shown in FIG. 4, the image-forming optical system 1 is telecentric on the object 0 side and the image I side. In addition, the wavefront disturbing device 5 is disposed at a position away from the field lens 4 by a distance a_(F) toward the object O, and the wavefront restoring device 6 is disposed at a position away from the field lens 4 by a distance b_(F) toward the image I.

In FIG. 4, reference sign f_(O) indicates the focal length of the image-forming lens 2, reference sign f_(T) indicates the focal length of the image-forming lens 3, reference signs F_(O) and F_(O)′ indicate focal positions of the image-forming lens 2, reference signs F_(T) and F_(T)′ indicate the focal positions of the image-forming lens 3, and reference signs II_(O), II_(A), and II_(B) indicate intermediate images.

Here, the wavefront disturbing device 5 need not necessarily be disposed in the vicinity of the pupil position PP_(O) of the image-forming lens 2, and, also, the wavefront restoring device 6 need not necessarily be disposed in the vicinity of the pupil position PP_(T) of the image-forming lens 3.

However, with regard to image formation by the field lens 4, the wavefront disturbing device 5 and the wavefront restoring device 6 must be disposed so as to have a mutually conjugate positional relationship, as indicated by Expression (1).

1/f _(F)=1/a _(F)+1/b _(F)  (1)

where f_(F) is the focal length of the field lens 4.

FIG. 5 is a diagram showing, in detail, the portion between the pupil position PP_(O) on the object O side and the wavefront restoring device 6 in FIG. 4.

Here, ΔL is a phase advance achieved, with reference to a ray that passes through a specific position (that is, a ray height), when light passes through an optical element.

In addition, ΔL_(O)(x_(O)) is a function that gives, with reference to the case in which light travels along an optical axis of wavefront disturbing device 5 (that is, x=0), a phase advance equal to that in the case in which light travels at an arbitrary ray height x_(O) in the wavefront disturbing device 5.

Furthermore, ur_(I)(x_(I)) is a function that gives, with reference to the case in which light travels along an optical axis of the wavefront restoring device 6 (that is, x=0), a phase advance equal to that in the case in which light travels at an arbitrary ray height x_(i) in the wavefront restoring device 6.

00_(O)(x_(O)) and ar_(I) (x_(I)) satisfy Expression (2) below.

Δ_(O)(x _(O))+ti _(I)(x _(I)=ti _(O)(x _(O))+ti _(I)(F·x _(O))=0  (2)

Here, β_(F) is a lateral magnification of the field lens 4 when the wavefront disturbing device 5 and the wavefront restoring device 6 are in a conjugate relationship, which is expressed in Expression (3) below.

When a single ray R enters such an image-forming optical system 1 and passes through a position x_(O) in the wavefront disturbing device 5, at that point, the ray is subjected to a phase modulation based on the function ΔL_(O)(x_(O)), and a disturbed ray Rc is generated due to refraction, diffraction, scattering, or the like. The disturbed ray Rc is projected by the field lens 4 to a position x_(I)=_(F)·x_(O) on the wavefront restoring device 6, together with components of the ray R that were not subjected to the phase modulation. By passing through the position x_(T), the projected ray is subjected to a phase modulation based on the function ΔL_(I)(a_(F)·x_(O))=−ΔL_(O)(x_(O)), and thus, the phase modulation applied thereto by the wavefront disturbing device 5 is cancelled out. By doing so, the ray is restored to a single ray R′ whose wavefront is not disturbed.

In the case in which the wavefront disturbing device 5 and the wavefront restoring device 6 are in a conjugate positional relationship and also possess the properties according to Expression (2), the ray that has been subjected to phase modulation by passing through a position in the wavefront disturbing device 5 passes through, without exception, a specific position in the wavefront restoring device 6, which is in one-to-one correspondence with the above-described position and at which the phase modulation that cancels out the phase modulation applied by the wavefront disturbing device 5 is applied. With the optical system shown in FIGS. 4 and 5, the above-described effects are exerted on the ray R regardless of the incident position x_(O) and the incident angle of the ray R in the wavefront disturbing device 5. Specifically, for all types of rays R, it is possible to make the intermediate image II unsharp and also to form a sharp final image I.

Note that, to use phase modulators having the same phase distribution as the wavefront disturbing device 5 and the wavefront restoring device 6, as in the present invention, the absolute value of the horizontal magnification β_(F) needs to be 1.

FIG. 6 shows a conventional image-forming optical system. With this image-forming optical system, light focused by the image-forming lens 2 at the object O side forms a sharp intermediate image II at the field lens 4 disposed at the intermediate-image-forming plane, and is subsequently focused by the image-forming lens 3 at the image I side, thus forming a sharp final image I.

With the conventional image-forming optical system, in the case in which there are blemishes, dust, or the like on a surface of the field lens 4 or there are defects, such as cavities or the like, inside the field lens 4, images of these foreign objects are superimposed on the sharp intermediate image formed at the field lens 4, which results in a problem in that the images of these foreign objects are also included when the final image I is formed.

In contrast, with the image-forming optical system 1 according to this embodiment, because an intermediate image II that has been made unsharp by the wavefront disturbing device 5 is formed at the intermediate-image-forming plane that is disposed at a position coinciding with the field lens 4, when the unsharp intermediate image II is made sharp by being subjected to the phase modulation by the wavefront restoring device 6, the images of foreign objects superimposed on the intermediate image II are made unsharp by being subjected to the same phase modulation. Therefore, it is possible to prevent the images of the foreign objects at the intermediate-image-forming plane from being superimposed on the sharp final image I.

In this case, by using the wavefront disturbing device 5 and the wavefront restoring device 6 having the same phase distribution, it is possible to simplify the manufacturing process and to reduce the cost, compared with a case where two types of phase modulators having different phase-modulation distributions have to be prepared.

Note that, in the above description, although the two image-forming lenses 2 and 3 have been described as being telecentrically disposed with respect to each other, their arrangement is not limited thereto, and similar effects are also achieved with a non-telecentric system.

In addition, although the function of the phase advance has been assumed to be a one-dimensional function, similar effects may also be achieved by employing a two-dimensional function instead.

In addition, spaces between the image-forming lens 2, the wavefront disturbing device 5, and the field lens 4 and spaces between the field lens 4, the wavefront restoring device 6, and the image-forming lens 3 need not necessarily be provided, and these devices may be optically coupled.

In addition, the individual lenses that form the image-forming optical system 1, namely, the image-forming lenses 2 and 3 and the field lens 4, are configured such that the image forming function and the pupil relay function are clearly divided therebetween; however, in an actual image-forming optical system, a configuration in which a single lens concurrently performs both the image forming function and the pupil relay function may also be employed. In such a case also, if the above-described conditions are satisfied, the wavefront disturbing device 5 can disturb the wavefront to make the intermediate image II unsharp, and the wavefront restoring device 6 can make the final image I sharp by canceling out the wavefront disturbance.

This embodiment can be modified as follows.

In this embodiment, as shown in FIG. 3, the wavefront disturbing device 5 and the wavefront restoring device 6 have a phase distribution including rectangular-wave-shaped phase-advancing regions 5 a and 6 a and phase-delaying regions 5 b and 6 b that are symmetrical to each other. Instead, in a first modification, for example, as shown in FIG. 7, the wavefront disturbing device 5 and the wavefront restoring device 6 may have a phase distribution including trapezoidal-wave-shaped phase-advancing regions 5 a and 6 a and phase-delaying regions 5 b and 6 b that are symmetrical to each other. In this case, as shown in FIG. 8, the wavefront disturbing device 5 and the wavefront restoring device 6 may be disposed such that they face each other and such that their positions are shifted from each other by half a period in the direction perpendicular to the optical axis, so that the light coming from the object O side and transmitted through the phase-advancing regions 5 a of the wavefront disturbing device 5 is transmitted through and exits from the phase-delaying regions 6 b of the wavefront restoring device 6, and so that the light coming from the object side and transmitted through the phase-delaying regions 5 b of the wavefront disturbing device 5 is transmitted through and exits from the phase-advancing regions 6 a of the wavefront restoring device 6.

Furthermore, the wavefront disturbing device 5 and the wavefront restoring device 6 may have phase distributions including phase-advancing regions 5 a and 6 a and phase-delaying regions 5 b and 6 b having wave shapes as shown in FIG. 9A to FIG. 9E. Specifically, the wave shapes of the phase-advancing regions 5 a and 6 a and the phase-delaying regions 5 b and 6 b may be symmetrical triangular-wave shapes, as shown in FIG. 9A, symmetrical sinusoidal-wave shapes, as shown in FIG. 9B, symmetrical deformed-wave shapes, as shown in FIG. 9C and FIG. 9D, or symmetrical sawtooth-wave shapes, as shown in FIG. 9E.

The phase-advancing regions 5 a and 6 a and the phase-delaying regions 5 b and 6 b in FIGS. 9A, 9B, 9D, and 9E are formed rotationally symmetrical to each other with respect to the average plane H, similarly to the phase-advancing regions 5 a and 6 a and the phase-delaying regions 5 b and 6 b shown in FIG. 3. The phase-advancing regions 5 a and 6 a and the phase-delaying regions 5 b and 6 b in FIG. 9C are formed symmetrical to each other with respect to the average plane H, such that their positions are shifted from each other by half a period.

Furthermore, in this embodiment, although the wavefront disturbing device 5 and the wavefront restoring device 6 have one-dimensional phase distribution characteristics, in a second modification, the wavefront disturbing device 5 and the wavefront restoring device 6 may have two-dimensional phase distribution characteristics.

For example, as shown in FIG. 10, the wavefront disturbing device 5 and the wavefront restoring device 6 may have a phase distribution in which rectangular-wave-shaped phase-advancing regions 5 a and 6 a and phase-delaying regions 5 b and 6 b that are symmetrical to each other are disposed in a checkered pattern. Alternatively, as shown in FIG. 11, in the wavefront disturbing device 5 and the wavefront restoring device 6, trapezoidal-wave-shaped phase-advancing regions 5 a and 6 a and phase-delaying regions 5 b and 6 b that are symmetrical to each other may be disposed in a checkered pattern. Furthermore, as shown in FIG. 12, triangular-wave-shaped, i.e., pyramid-shaped, phase-advancing regions 5 a and 6 a and phase-delaying regions 5 b and 6 b that are symmetrical to each other may be disposed in a checkered pattern.

This makes it possible to more complexly unsharpen the intermediate image II than in the case where the wavefront disturbing device 5 and the wavefront restoring device 6 having one-dimensional phase distribution characteristics are used.

Furthermore, in this embodiment, the wavefront disturbing device 5 and the wavefront restoring device 6 that apply phase modulation to the wavefront of light by means of the surface shape of the optical medium have been described as examples of the first phase modulator and the second phase modulator. Instead, in a third modification, as shown in FIG. 13, the first phase modulator and the second phase modulator may apply phase modulation to the wavefront of light by means of the interface shapes of a plurality of optical media.

FIG. 13 shows, as an example, a wavefront disturbing device 5′ and a wavefront restoring device 6′ each formed of an optical medium n_(A) and an optical medium n_(B) having different refractive indices. The wavefront disturbing device 5′ and the wavefront restoring device 6′ have the same phase distribution including wave-shaped phase-advancing regions 5 a and 6 a and phase-delaying regions 5 b and 6 b that are defined by the shapes of the interface between the optical medium n_(A) and the optical medium n_(B) and are symmetrical to each other. The phase-advancing regions 5 a and 6 a and the phase-delaying regions 5 b and 6 b are formed rotationally symmetrical to each other with respect to the average plane H.

This makes it possible to apply more precise phase modulation to the wavefront of light than in the case where a single optical medium having the same shape accuracy is used as the phase modulators. Furthermore, because the shape accuracy of the optical media required to achieve the same phase-modulation precision is lower than that in the case where a single optical medium is used as the phase modulators, it is possible to manufacture the phase modulators at even lower cost.

When the wavefront disturbing device 5′ and the wavefront restoring device 6′ of this modification are incorporated in an actual optical system, a configuration in which these elements are disposed such that the common optical medium in the wavefront disturbing device 5′ and the wavefront restoring device 6′ faces the field lens 4 (for example, a configuration in which both the wavefront disturbing device 5′ and the wavefront restoring device 6′ are disposed such that the optical medium n_(A) faces the field lens 4) is more desirable, from the standpoint of the wave-recovery precision.

Furthermore, in this embodiment, although the wavefront disturbing device 5 and the wavefront restoring device 6 having a phase-modulation distribution in which a plurality of pairs of the phase-advancing region 5 a and the phase-delaying region 5 b and a plurality of pairs of the phase-advancing region 6 a and the phase-delaying region 6 b, respectively, are periodically disposed have been described as examples of the first phase modulator and the second phase modulator, in a fourth modification, a phase-modulation distribution including one pair of the phase-advancing region 5 a and the phase-delaying region 5 b and one pair of the phase-advancing region 6 a and the phase-delaying region 6 b is also possible.

Next, an observation apparatus 10 according to a first embodiment of the present invention will be described below with reference to the drawings.

As shown in FIG. 14, the observation apparatus 10 according to this embodiment is provided with a light source 11 that generates non-coherent illumination light; an illumination optical system 12 that irradiates an observation subject A with the illumination light coming from the light source 11; an image-forming optical system 13 that focuses light coming from the observation subject A; and an image-acquisition device (photo-detector) 14 that captures the light focused by the image-forming optical system 13 and acquires an image thereof.

The illumination optical system 12 is provided with focusing lenses 15 a and 15 b that focus the illumination light coming from the light source 11 and an objective lens 16 that irradiates the observation subject A with the illumination light focused by the focusing lenses 15 a and 15 b.

In addition, this illumination optical system 12 is a so-called Koehler illumination optical system, and the focusing lenses 15 a and 15 b are disposed so that a light emission surface of the light source 11 and a pupil plane of the objective lens 16 are conjugate with each other.

The image-forming optical system 13 is provided with the above-described objective lens (image-forming lens) 16 that is disposed on the object side and that collects observation light (for example, reflected light) emitted from the observation subject A; a wavefront disturbing device (first phase modulator) 17 that disturbs the wavefront of the observation light collected by the objective lens 16; a first beam splitter 18 that splits off the light whose wavefront has been disturbed from the illumination optical path from the light source 11; a first intermediate-image-forming-lens pair 19 having lenses that are that are disposed so as to have a space therebetween in the optical-axis direction; a second beam splitter 20 that deflects, by 90i, the light that has passed through individual lenses 19 a and 19 b of the first intermediate-image-forming-lens pair 19; a second intermediate-image-forming lens 21 that forms an intermediate image by focusing the light that has been deflected by the second beam splitter 20; an optical-path-length varying means 22 that is disposed at an intermediate-image-forming plane of the second intermediate-image-forming lens 21; an intermediate-image-forming lens pair 24 that focuses the light returned by the optical-path-length varying means 22 and transmitted through the intermediate-image-forming lens 21 and the second beam splitter 20 to form an intermediate image; an image-forming lens 25 that focuses the light having passed through lenses 24 a and 24 b in the intermediate-image-forming lens pair 24 to form the final image; and a wavefront restoring device (second phase modulator) 23 disposed between the intermediate-image-forming lens pair 24 and the image-forming lens 25.

The image-acquisition device 14 is, for example, a two-dimensional image sensor, such as a CCD or a CMOS, is provided with an image-acquisition surface 14 a disposed at a position at which a final image is formed by the image-forming lens 24. The image-acquisition device 14 is configured so that a two-dimensional image of the observation subject A can be acquired by capturing the incident light.

The wavefront disturbing device 17 is disposed in the vicinity of the pupil position of the objective lens 16. The wavefront disturbing device 17 is formed of an optically transparent material that allows light to pass therethrough, and is configured so that, when light passes therethrough, a phase modulation is applied to the wavefront of the light in accordance with depressions and protrusions on the surface of the optically transparent material. The wavefront restoring device 23 is also formed of an optically transparent material that allows light to pass therethrough, and is configured so as that, when light passes therethrough, a phase modulation is applied to the wavefront of the light in accordance with depressions and protrusions on the surface of the optically transparent material.

Similarly to the above-described wavefront disturbing device 5 and the wavefront restoring device 6, the wavefront disturbing device 17 and the wavefront restoring device 23 have the same phase distribution including a wave-shaped phase-advancing region and phase-delaying region that are symmetrical to each other, and are paired such that through the corresponding phase-advancing region and phase-delaying region having opposite wave shapes. Hence, in the wavefront disturbing device 17 and the wavefront restoring device 23, as a result of light whose wavefront has been disturbed by being transmitted through one of the wavefront disturbing device 17 and the wavefront restoring device 23 being transmitted through the other of the wavefront restoring device 23 and the other wavefront disturbing device 17, the disturbance applied can be cancelled out.

In this embodiment, the wavefront disturbing element 17 applies the necessary wavefront disturbance by allowing the observation light from the observation object A to be transmitted therethrough. Furthermore, by making the observation light reflected by the optical-path-length varying means 22 so as to be folded back pass therethrough twice while the light travels in a reciprocating manner, the wavefront restoring device 23 is configured so as to apply, to the wavefront of the light, the phase modulation that cancels out the wavefront disturbance applied by the wavefront disturbing device 17.

The optical-path-length varying means 22, serving as an optical-axis (Z-axis) scanning system, includes a flat mirror 22 a that is disposed perpendicularly to the optical axis and an actuator 22 b that displaces the flat mirror 22 a in the optical-axis direction. When the flat mirror 22 a is displaced in the optical-axis direction by actuating the actuator 22 b of the optical-path-length varying means 22, the optical-path length between the second intermediate-image-forming lens 21 and the flat mirror 22 a is changed, and, by doing so, the position in the observation subject A that is conjugate with the image-acquisition surface 14 a, that is, the front focal-point position of the objective lens 16, is changed in the optical-axis direction.

In order to observe the observation subject A by using the thus-configured observation apparatus 10 according to this embodiment, the illumination light coming from the light source 11 is radiated onto the observation subject A by means of the illumination optical system 12. The observation light emitted from the observation subject A is collected by the objective lens 16, passes through the first beam splitter 18 and the intermediate-image-forming lens pair 19, and is deflected by 90e by the second beam splitter 20. Then, the observation light is reflected, so as to be folded back, by the flat mirror 22 a of the optical-path-length varying means 22 via the second intermediate-image-forming lens 21, and is transmitted through the wavefront restoring device 23 via the beam splitter 20 and the intermediate-image-forming lens pair 24. As a result, the final image formed by the image-forming lens 25 is acquired by means of the image-acquisition device 14.

By moving the flat mirror 22 a in the optical axis direction by actuating the actuator 22 b of the optical-path-length varying means 22, the optical path length between the second intermediate-image-forming lens 21 and the flat mirror 22 a can be changed. By doing so, the front focal-point position of the objective lens 16 can be moved and scanned in the optical-axis direction. Thus, by capturing the observation light at different focal-point positions, it is possible to acquire a plurality of images that are focused at different positions of the observation subject A in the depth direction. Furthermore, by applying high-frequency emphasizing processing after combining the plurality of images by taking an arithmetic average thereof, it is possible to acquire an image having a large depth of field.

In this case, an intermediate image is formed by the second intermediate-image-forming lens 21 in the vicinity of the flat mirror 22 a of the optical-path-length varying means 22. This intermediate image is unsharpened by the wavefront disturbance applied by passing through the wavefront disturbing device 17. Then, the light that has formed the unsharp intermediate image is focused by the second intermediate-image-forming lens 21 and the intermediate-image-forming lens pair 24 and is, subsequently, made to pass through the wavefront restoring device 23 again, which completely cancels out the wavefront disturbance thereof.

As a result, with the observation apparatus 10 according to this embodiment, there is an advantage in that, even if foreign objects such as blemishes, dust or the like exist on the surface of the flat mirror 22 a, it is possible to prevent images of the foreign objects from being captured in a final image by being superimposed thereon, and that it is also possible to acquire a sharp image of the observation subject A.

Similarly, although the intermediate image formed by the first intermediate-image-forming-lens pair 19 also undergoes large changes in the optical-axis direction when the focal-point positions on the observation subject A are moved in the optical-axis direction, as a result of these changes, even if the intermediate image coincides with the position of the first intermediate-image-forming-lens pair 19, or even in the case in which another optical element additionally exits in the area in which the changes occur, because the intermediate image has been made unsharp, it is possible to prevent the images of the foreign objects from being captured in the final image by being superimposed thereon. In this embodiment, when the above-described scanning system is incorporated, no noise image is generated in any of the optical elements disposed in the image-forming optical system even if the light moves in the Z-axis direction. Furthermore, by using the wavefront disturbing element 17 and the wavefront recovery element 23 having the same phase distribution, there is an advantage in that it is possible to simplify the manufacturing process and to reduce the cost, compared with a case where two types of phase-modulating elements having different phase-modulation distributions have to be prepared.

Next, an illumination apparatus 28 and an observation apparatus 30 according to a second embodiment of the present invention will be described below with reference to the drawings.

In describing this embodiment, the same reference signs are assigned to portions having the same configurations as those of the observation apparatus 10 according to the first embodiment described above, and descriptions thereof will be omitted.

As shown in FIG. 15, an observation apparatus 30 according to this embodiment includes: the illumination apparatus 28 having a laser light source 31; and an image-forming optical system 32 that focuses the laser beams coming from the laser light source 31 on the observation subject A and that also collects light coming from the observation subject A; an image-acquisition device (photo-detector) 33 that captures the light collected by the image-forming optical system 32; and a Nipkow-disk-type confocal optical system 34 that is disposed between the light source 31, and the image-acquisition device 33 and image-forming optical system 32.

The Nipkow-disk-type confocal optical system 34 is provided with two disks 34 a and 34 b that are disposed parallel to each other with a space therebetween and an actuator 34 c that rotates the disks 34 a and 34 b at the same time. Numerous microlenses (not shown) are arrayed on the disk 34 a on the laser light source 31 side, and the disk 34 b on the object side is provided with numerous pinholes (not shown) at positions that correspond to the individual microlenses. In addition, a dichroic mirror 34 d that splits light that has passed through the pinholes is secured in the space between the two disks 34 a and 34 b. The light split off by the dichroic mirror 34 d is focused by the focusing lens 35, a final image is formed on an image-acquisition surface 33 a of the image-acquisition device 33, and thus, an image is acquired.

In the image-forming optical system 32, by means of the beam splitter 36, the optical path for irradiating the observation subject A with the light that has passed through the pinholes of the Nipkow-disk-type confocal optical system 34 and the optical path through which the light generated at the observation subject A enters the pinholes of the Nipkow-disk-type confocal optical system 34 are exactly the same.

The operation of the thus-configured observation apparatus 30 according to this embodiment will be described below.

In the observation apparatus 30 according to this embodiment, the light emitted from the pinholes in the Nipkow-disk-type confocal optical system 34 and entering the image-forming optical system 32 via the image-forming optical system 25, the phase modulator 23, and the intermediate-image-forming lens pair 24 is transmitted through the beam splitter 36, is focused by the second intermediate-image-forming lens 21, and is reflected, so as to turn around, by the flat mirror 22 a of the optical-path-length varying means 22. Then, after having passed through the second intermediate-image-forming lens 21, the light is deflected by 90 by the beam splitter 36, is transmitted through the first intermediate-image-forming lens pair 19 and the phase modulator 17, and is focused on the observation object A by the objective lens 16.

In this embodiment, the phase modulator 23, through which the laser beam passes twice first serves as a wavefront disturbing device that disturbs the wavefront of the laser beam, and the phase modulator 17 through which the laser beam subsequently passes once serves as a wavefront restoring device that applies the phase modulation that cancels out the wavefront disturbance applied by the phase modulator 23.

Therefore, although an image of the light sources that are formed like numerous point sources of light by the Nipkow-disk-type confocal optical system 34 is formed as an intermediate image on the flat mirror 22 a by the second intermediate-image-forming lens 21, because the intermediate image formed by the second intermediate-image-forming lens 21 is made unsharp by passing through the phase modulator 23 once, it is possible to prevent a problem by the images of the foreign objects existing in the intermediate-image-forming plane are superimposed on the final image.

In addition, because the disturbance applied to the wavefront by passing through the phase modulator 23 twice is canceled out by passing through the phase modulator 17, it is possible to form a sharp image of the numerous point sources of light at the observation subject A. Then, high-speed scanning can be performed by moving the image of the numerous point sources of light formed at the observation subject A in the XY direction that intersects the optical axis by rotating the disks 34 a and 34 b by actuating the actuator 34 c of the Nipkow-disk-type confocal optical system 34.

The light, e.g., fluorescence, generated at the position in the observation object A where the image of point light sources is formed is collected by the objective lens 16 and is transmitted through the phase modulator 17 and the first intermediate-image-forming lens pair 19. Then, the light is deflected by 90 ediate-image-forming 16 o, is focused by the second intermediate-image-forming lens 21, and is reflected, so as to turn around, by the flat mirror 22 a. Thereafter, the light is focused again by the second intermediate-image-forming lens 21, is transmitted through the beam splitter 36, is focused by the intermediate-image-forming lens pair 24, and is transmitted through the phase modulator 23. Then, the light is focused by the image-forming lens 25 and forms an image at the position of the pinholes in the Nipkow-disk-type confocal optical system 34.

The light that has passed through the pinholes is split off from the optical path from the laser light source 31 by the dichroic mirror 34 d, is focused by the focusing lens 35, and forms the final image at the image-acquisition surface 33 a of the image-acquisition device 33. In this case, the phase modulator 17 through which the fluorescence generated at the observation subject in the form of numerous points passes serves as a wavefront disturbing device as in the first embodiment, and the phase modulator 23 serves as a wavefront restoring device.

Hence, the fluorescence whose wavefront has been disturbed by passing through the phase modulator 17 forms an unsharp intermediate image on the flat mirror 22 a. Then, the fluorescence whose wavefront disturbance has completely been cancelled out by passing through the phase modulator 23 forms an image at the pinholes of the Nipkow-disk-type confocal optical system 34. The fluorescence after passing through the pinholes is split off by the dichroic mirror 34 d, is focused by the focusing lens 35, and forms a sharp final image on the image-acquisition surface 33 a of the image-acquisition device 33.

By doing so, with the observation apparatus according to this embodiment, there is an advantage in that, as an illumination apparatus that radiates laser beams onto the observation subject A and also as an observation apparatus with which fluorescence generated at the observation subject A is captured, it is possible to acquire a sharp final image while preventing images of foreign objects at an intermediate-image-forming plane from being superimposed on the final image by making the intermediate image unsharp. In this embodiment, when the above-described scanning system is incorporated, no noise image is generated even if the light moves in the Z-axis direction in any of the optical elements disposed in the image-forming optical system.

Next, an illumination apparatus 38 and an observation apparatus 40 according to a third embodiment of the present invention will be described below with reference to the drawings.

In describing this embodiment, the same reference signs are assigned to portions having the same configurations as those of the observation apparatus 30 according to the second embodiment described above, and descriptions thereof will be omitted.

As shown in FIG. 16, the observation apparatus 40 according to this embodiment is a laser-scanning confocal observation apparatus.

This observation apparatus 40 is provided with an illumination apparatus 38 having a laser light source 41 and an image-forming optical system 42 that focuses laser beams coming from the laser light source 41 on the observation subject A and that also collects light coming from the observation subject A; a confocal pinhole 43 that allows fluorescence collected by the image-forming optical system 42 to pass therethrough; and a photo-detector 44 that detects the fluorescence that has passed through the confocal pinhole 43.

The image-forming optical system 42 is provided with a beam expander 45 that expands the beam diameter of a laser beam, a dichroic mirror 46 that deflects the laser beam and that allows fluorescence to pass therethrough, a galvanometer mirror 47 that is disposed in the vicinity of a position that is conjugate with the pupil of the objective lens 16, and a third intermediate-image-forming-lens pair 48, which are different components from those of the observation apparatus 30 according to the second embodiment. Furthermore, a phase modulator 23 that disturbs the wavefront of the laser beam is disposed in the vicinity of pupil position of the objective lens 16. In the figures, reference sign 49 indicates a mirror.

The operation of the thus-configured observation apparatus 40 according to this embodiment will be described below.

With the observation apparatus 40 according to this embodiment, the laser beam emitted from the laser light source 41, whose diameter is expanded by the beam expander 45, is deflected by the dichroic mirror 46, and is two-dimensionally scanned by the galvanometer mirror 47, after which the laser beam passes through the phase modulator 23 and the third intermediate-image-forming-lens pair 48, and enters the beam splitter 36. The processes after entering the beam splitter 36 are the same as those of the observation apparatus 30 according to the second embodiment.

Specifically, because the laser beam forms an intermediate image at the flat mirror 22 a of the optical-path-length varying means 22 after the wavefront thereof is disturbed by the phase modulator 23, the intermediate image is made unsharp, and thus, it is possible to prevent the images of foreign objects that exist in the intermediate-image-forming plane from being superimposed thereon. In addition, because the wavefront disturbance is cancelled out by the phase modulator 17 disposed at the pupil position of the objective lens 16, it is possible to form a sharp final image at the observation subject A. In addition, the image formation depth of the final image can be arbitrarily adjusted by the optical-path-length varying means 22.

On the other hand, fluorescence generated at a position in the observation subject A at which the laser beam forms the final image is collected by the objective lens 16 and is transmitted through the phase modulator 17. The fluorescence travels along the optical path in the reverse route from that traveled by the laser beam, is deflected by the beam splitter 36, passes through the third intermediate-image-forming-lens pair 48, the phase modulator 23, the galvanometer mirror 47, and the dichroic mirror 46, and is focused at a confocal pinhole 43 by the image-forming lens 24. Then, only the fluorescence that has passed through the confocal pinhole 43 is detected by the photo-detector 44.

In this case also, because the fluorescence collected by the objective lens 16 forms an intermediate image after the wavefront thereof is disturbed by the phase modulator 17, the intermediate image is made unsharp, and thus, it is possible to prevent the images of foreign objects that exist in the intermediate-image-forming plane from being superimposed thereon. Also, because the wavefront disturbance is cancelled out by passing through the phase modulator 23, it is possible to form a sharp image at the confocal pinhole 43, and it is possible to efficiently detect the fluorescence generated at the position in the observation subject A at which the laser beam forms the final image. As a result, there is an advantage in that it is possible to acquire a high-resolution, bright confocal image. In this embodiment, when the above-described scanning system is incorporated, no noise image is generated even if the light moves in the Z-axis direction in any of the optical elements disposed in the image-forming optical system.

Note that, in this embodiment, although a laser-scanning confocal observation apparatus has been described as an example, alternatively, the present invention may be applied to a laser-scanning multi-photon-excitation observation apparatus, as shown in FIG. 17.

In this case, an ultrashort pulsed laser light source may be employed as the laser light source 41, the dichroic mirror 46 may be eliminated from the original position, and the dichroic mirror 46 may be employed instead of the mirror 49.

With an observation apparatus 50 in FIG. 17, it is possible to make the final image sharp by making the intermediate image unsharp by using its function as an illumination apparatus that radiates an ultrashort pulsed laser beam onto the observation subject A. With regard to the fluorescence generated at the observation subject A, the fluorescence is collected by the objective lens 16, passes through the phase modulator 17 and the dichroic mirror 46, is subsequently focused by the focusing lens 51 without forming an intermediate image, and is directly detected by the photo-detector 44.

In addition, in the individual embodiments described above, by means of the optical-path-length varying means 22 that changes the optical-path length via the movement of the flat mirror that folds back the optical path, the front focal-point position of the objective lens 16 is changed in the optical-axis direction. Alternatively, an observation apparatus 60 may be configured by employing, as the optical-path-length varying means, a unit that changes the optical-path length by moving a lens 61 a, which is one of lenses 61 a and 61 b that form an intermediate-image-forming optical system 61, in the optical-axis direction by using the actuator 62, as shown in FIG. 18. In the figures, reference sign 63 indicates another intermediate-image-forming optical system.

In addition, as shown in FIG. 19, the present invention may be configured such that another intermediate-image-forming optical system 80 is disposed between two galvanometer mirrors 47 that constitute a two-dimensional light scanner, and the two galvanometer mirrors 47 are precisely disposed in an optically conjugate positional relationship relative to the phase modulators 17 and 23 and an aperture stop 81 disposed at the pupil of the objective lens 16.

In addition, a spatial light modulator (SLM) 64, such as a reflecting-type LCOS, may be employed as the optical-path-length varying means, as shown in FIG. 20. By doing so, it is possible to change the front focal-point position of the objective lens 16 in the optical-axis direction at high speed by changing the phase modulation to be applied to the wavefront at high speed by controlling liquid crystals of the LCOS. In the figures, reference sign 52 denotes an intermediate-image-forming lens pair that focuses laser light, whose beam diameter has been increased by the beam expander 45, to form an intermediate image, and reference signs 65 are mirrors. In this case, the phase-modulating element 17 may be disposed between the beam splitter 36 and the objective lens 16, and the phase-modulating element 23 may be disposed between the beam expander 45 and the intermediate-image-forming lens pair 52.

In addition, instead of the spatial light modulator 64 such as a reflecting-type LCOS, a spatial light modulator 66 such as a transmitting-type LCOS may be employed, as shown in FIG. 21. Because the mirror 65 can be eliminated, as compared with the case in which the reflecting-type LCOS is employed, the configuration can be simplified.

As a means of moving the focal-point position in the observation subject A in the optical-axis direction other than the individual examples that have been described (the optical-path-length varying means 22, or the intermediate-image-forming optical system 61 and the actuator 62, or a reflecting-type spatial light modulator 64, or the transmitting-type spatial light modulator 66), it is possible to use various types of variable-power optical elements, which are known as active optical elements, including, first of all, as ones that have mechanically movable portions, a variable-shape mirror (DFM: Deformable Mirror) and a variable-shape lens employing liquid or gel. Also, examples of similar devices that do not have mechanically movable portions include, among others, a liquid-crystal lens and a potassium tantalate niobate (KTN: KTa_(1-x)Nb_(x)O₃) crystal lens that control the refractive index of a medium by means of an electric field, and, additionally, a lens in which a cylindrical-lens effect in an acoustic optical deflector (AOD/Acousto-Optical Deflector) is applied.

As has been described above, in the embodiments of the present invention in the form of microscopes, some means of moving the focal-point position in the observation subject A in the optical-axis direction is included in all cases. Furthermore, with these means of moving the focal-point position in the optical-axis direction, as compared with means employed in a conventional microscope designed for the same purpose (namely, to move either the objective lens 16 or the observation subject in the optical-axis direction), it is possible to considerably increase the operating speed because a low-mass object to be driven is used or a physical phenomenon whose response speed is high is utilized.

This affords an advantage in that it is possible to detect phenomena occurring at higher speed in an observation subject (for example, living biological tissue specimen).

In a reference embodiment of the invention, serving as a reference example of the present invention, when the spatial light modulators 64 and 66, such as a transmitting-type or a reflecting-type LCOS, are employed, it is possible to make the spatial light modulators 64 and 66 perform the function of the phase modulator 23. By doing so, it is possible to omit the phase modulator 23 that serves as a wavefront disturbing device, and thus, there is an advantage in that it is possible to simplify the configuration.

In addition, although the above-described example is a form in which the phase modulator 23 is omitted in a combination of the spatial light modulator and a laser-scanning multi-photon-excitation observation apparatus, in a similar manner, in the reference embodiment of the invention, serving as a reference example of the present invention, it is also possible to omit the phase modulator 23 in a combination of the spatial light modulator and a laser-scanning confocal observation apparatus. Specifically, in FIG. 20 and FIG. 21, the mirror 49 can be employed instead of the beam splitter 36, the dichroic mirror 46 can be employed between the beam expander 45 and the spatial light modulators 64 and 66, thus forming a branch optical path; and, furthermore, given that the image-forming lens 24, the confocal pinhole 43, and the photo-detector 44 are employed, it is possible to make the spatial light modulators 64 and 66 perform the function of the phase modulator 23. The spatial light modulators 64 and 66 in this case serve as wavefront disturbing devices with respect to a laser beam coming from the laser light source 41, disturbing the wavefront thereof, and, on the other hand, serve as wavefront restoring devices with respect to fluorescence coming from the observation subject A, canceling out the wavefront disturbance applied thereto by the phase modulator 17.

As shown in FIG. 22, cylindrical lenses 68 and 69 may be employed as phase modulators in the above-described reference embodiment, for example.

In this case, with the cylindrical lens 68, because an intermediate image in the form of a point image is elongated into a linear shape due to astigmatism, it is possible to make the intermediate image unsharp by means of this effect. Furthermore, it is possible to make the final image sharp by means of the cylindrical lens 69, whose shape is complementary to that of the cylindrical lens 17.

In the case shown in FIG. 22, either a convex lens or a concave lens may be used as a wavefront disturbing device or may be used as a wavefront restoring device.

The effect of using cylindrical lenses 5 and 6 as the phase modulators will be described below in detail. FIG. 23 shows an example in which the cylindrical lenses 5 and 6 are used as the phase modulators in FIG. 4 and FIG. 5.

Here, the following conditions are set in particular.

(a) A cylindrical lens having a power t_(Ox) in the X-direction is used as the object-O-side phase modulator (wavefront disturbing device) 5. (b) A cylindrical lens having a power t_(Ix) in the X-direction is used as the image-I-side phase modulator (wavefront restoring device) 6. (c) A position (ray height) of an on-axis ray R_(X) on the X-Z plane in the cylindrical lens 5 is assumed to be x_(O). (d) A position (ray height) of an on-axis ray R_(X) on the X-Z plane in the cylindrical lens 6 is assumed to be x_(I).

In FIG. 23, reference signs II_(0X) and II_(0Y) indicate intermediate images.

Before describing the effects of this example, the relationship between the phase modulation level and the optical power based on Gaussian optics will be described by using FIG. 24.

In FIG. 24, assuming that the lens thickness at the height (distance from the optical axis) x is d(x) and that the lens thickness at the height 0 (on the optical axis) is d₀, the optical-path length L(x) between the entrance-side tangential plane and the exit-side tangential plane extending along a ray at the height x is expressed by Expression (4) below.

L(x)=(d ₀ −d(x))+n·d(x)  (4)

The difference between the optical-path length L(x) at the height x and the optical-path length L(0) at the height 0 (on the optical axis) is expressed by Expression (5) below, when the thin-lens approximation is used.

L(x)−L(0)=(−x ²/2)(n−1)(1/r ₁−1/r ₂)  (5)

Regarding the optical-path-length difference L(x)−L(0) described above, the absolute value thereof is equal to the phase advance of light exiting at the height x relative to light exiting at the height 0, and the sign thereof is reversed. Therefore, the above-described phase advance is expressed by Expression (6) below, which has an opposite sign to Expression (5).

L(0)−L(x)=(x ²/2)(n−1)(1/r ₁−1/r ₂)  (6)

On the other hand, the optical power d phase advance is expressed by Expression (6) below, which the optical power

d₁−1/r₂)  (7)

Therefore, based on Expressions (6) and (7), the relationship between the phase advance L(0)-L(x) and the optical power pparadetermined by Expression (8) below.

L(0)−L(x)=)·x ²/2  (8)

Here, let us return to describing FIG. 13.

The phase advance n_(Oc) experienced by the on-axis ray R_(x) on the X-Z plane in the cylindrical lens 5 relative to an on-axis principal ray, that is, a ray R_(A) traveling along the optical axis, is expressed by Expression (9) below based on Expression (8).

Δo _(Oc)(x _(O))=L _(Oc)(0)−L _(Oc)(x _(o))=−_(Ox) ·x _(O) ²/2  (9)

Here, L_(Oc)(x_(O)) is a function of the optical-path length between the entrance-side tangential plane and the exit-side tangential plane, extending along a ray at the height x_(O) in the cylindrical lens 5.

Similarly, the phase advance ce_(Ic) experienced by the on-axis ray R_(x) on the X-Z plane in the cylindrical lens 6 relative to the on-axis principal ray, that is, the ray R_(A) traveling along the optical axis, is expressed by Expression (10) below.

Δt _(Ic)(x _(I))=L _(Ic)(0)−L _(Ic)(x _(I))=−_(Ix) ·x _(I) ²/2  (10)

Here, L_(Ic)(x_(I)) is a function of the optical-path length between the entrance-side tangential plane and the exit-side tangential plane, extending along a ray at the height x_(I) in the cylindrical lens 6.

When the relationships expressed in Expressions (9) and (10) and (x_(I)/x_(O))²=n_(F) ² are applied to the above-described Expression (2), in this example, conditions for the cylindrical lens 5 to perform the function of disturbing a wavefront and those for the cylindrical lens 6 to perform the function of restoring a wavefront are determined as indicated by Expression (11).

ψ_(Ox) /x _(Ix) =−p _(F) ²  (11)

Specifically, it is necessary that the values of y_(Ox) and a_(Tx) have signs that are opposite from each other, and, also, that the ratio of their absolute values is proportional to the square of the lateral magnification of the field lens 4.

Note that, although the above descriptions are based on the on-axis ray, so long as the above-described conditions are satisfied, the cylindrical lenses 5 and 6 also perform the functions of disturbing a wavefront and restoring a wavefront in a similar manner for an off-axis ray.

In addition,

Furthermore, in the above-described respective embodiments of the present invention, one-dimensional binary diffraction gratings, as shown in FIG. 25, may be employed as the phase modulators 5, 6, 17, and 23 (shown as the phase modulators 5 and 6 in the drawing), instead of the cylindrical lenses. In the above-described reference embodiments, serving as reference examples of the present invention, one-dimensional sine-wave diffraction gratings, as shown in FIG. 26, free-curved surface lenses, as shown in FIG. 27, conical lenses, as shown in FIG. 28, or concentric binary diffraction gratings, as shown in FIG. 29, may be employed. The concentric-circle type diffraction gratings are not limited to a binary type, and any arbitrary configuration, such as a blazed type or a sinusoidal type, may be employed.

Here, the case in which the diffraction gratings 5 and 6 are employed as wavefront modulating devices will be described below in detail.

In an intermediate image II in this case, a single point image is separated into a plurality of point images by diffraction. Due to this effect, the intermediate image II is made unsharp, and thus, it is possible to prevent images of foreign objects in the intermediate-image-forming plane from appearing in the final image by being superimposed thereon.

For the case in which the diffraction gratings 5 and 6 are employed as phase modulators, an example of a preferable route for an on-axis principal ray, that is, the ray R_(A) traveling along the optical axis, is shown in FIG. 30, and, in addition, an example of a preferable route for the on-axis ray R_(X) is shown in FIG. 31. In these figures, although the rays R_(A) and R_(X) are separated into a plurality of diffracted rays via the diffraction grating 5, they are restored into a single ray, as was originally the case, by passing through the diffraction grating 6.

In this case also, by satisfying the above-described Expressions (1) to (3), it is possible to achieve the above-described effects.

Here, following FIGS. 30 and 31, it is possible to describe Expression (2) in a different manner such that “the sum of phase modulations the diffraction gratings 5 and 6 apply to a single on-axis ray R_(x) is always equal to the sum of phase modulations the diffraction gratings 5 and 6 apply to the on-axis principal ray R_(A)”.

In addition, in the case in which the diffraction gratings 5 and 6 have periodic structures, if the shapes (that is, phase modulation properties) thereof satisfy Expression (2) in a region corresponding to one period, it is possible to assume that Expression (2) is similarly satisfied in other regions.

Therefore, center portions of the diffraction gratings 5 and 6, that is, regions in the vicinity of the optical axis, will be focused on in the following description. FIG. 32 is a diagram showing details of the center portion of the diffraction grating 5, and FIG. 33 is a diagram showing details of the center portion of the diffraction grating 6.

Here, the following descriptions are the conditions for the diffraction gratings 5 and 6 to satisfy Expression (2).

Specifically, a modulation period p_(I) of the diffraction grating 6 must be equal to a modulation period p_(O) of the diffraction grating 5 projected by the field lens 4. Also, a modulation phase of the diffraction grating 6 must be reversed with respect to a modulation phase of the diffraction grating 5 projected by the field lens 4; and the magnitude of the phase modulation by the diffraction grating 5 and the magnitude of the phase modulation by the diffraction grating 6 must be equal to each other in terms of absolute values.

First, the conditions for the period p_(I) and the projected period p_(O) to be equal to each other are expressed by Expression (12).

p _(I) =|p _(F) |·p _(O)  (12)

Next, in order for the modulation phase of the diffraction grating 6 to be reversed with respect to the projected modulation phase of the diffraction grating 5, in addition to satisfying the above-described Expression (12), for example, the diffraction grating 5 needs to be disposed so that one of the centers of protruding regions thereof is aligned with the optical axis and also the diffraction grating 6 needs to be disposed so that one of the centers of depressed regions thereof is aligned with the optical axis. FIG. 32 and FIG. 33 show merely one example of such arrangements.

Finally, conditions for the magnitude of the phase modulation by the diffraction grating 6 and the magnitude of the phase modulation by the diffraction grating 5 to be equal to each other in terms of absolute values thereof are determined.

Based on optical parameters (the thickness t_(Oc) of the protruding regions, the thickness t_(Ot) of the depressed regions, and the refractive index n_(O)) of the diffraction grating 5, a phase advance Δp_(Odt) experienced by the on-axis ray R_(x) that passes through one of the depressed regions of the diffraction grating 5 relative to the ray R_(A) that travels along the optical axis (that passes through one of the protruding regions) is expressed by Expression (13) below.

ΔL _(Odt) =n _(O) ·t _(Oc)−(n _(O) ·t _(Ot)+(t _(Oc) −t _(Ot)))=(n _(O)−1)(t _(Oc) −t _(Ot))  (13)

Similarly, based on optical parameters (the thickness t_(Ic) of the protruding regions, the thickness t_(It) of the depressed regions, and the refractive index n_(I)) of the diffraction grating 6, a phase advance Δp_(Idt) experienced by the on-axis ray R_(X) that passes through one of the protruding regions of the diffraction grating 6 relative to the ray R_(A) that travels along the optical axis (that passes through one of the depressed regions) is expressed by Expression (14) below.

ΔL _(Idt)=(n _(I) −t _(It)+(t _(Ic) −t _(It)))−n _(I) ·t _(Ic)=−(n _(I)−1)(t _(Ic) −t _(It))  (14)

In this case, because the value of ΔI_(Odt) is positive, and the value of au_(Idt) is negative, the condition for the absolute values of the two to be equal to each other is expressed by Expression (15) below.

Δs _(Odt) +te _(Idt)=(n _(O)−1)(t _(Oc) −t _(Ot))−(n _(I)−1)(t _(Ic) −t _(It))=0  (15)

Note that, although the above descriptions are based on the on-axis ray, so long as the above-described condition is satisfied, the diffraction grating 5 performs the function of disturbing a wavefront, and the diffraction grating 6 also performs the function of restoring a wavefront for an off-axis ray also.

In addition, although the cross-sectional shape of the diffraction gratings 5 and 6 is assumed to be trapezoidal in the above descriptions, it is needless to say that similar functions can also be performed with other shapes.

Moreover, in reference embodiments of the invention, serving as reference examples of the present invention, spherical aberration devices, as shown in FIG. 34, irregular-shaped devices, as shown in FIG. 35, a reflective wavefront modulating element combined with a transmissive spatial light modulator 64, as shown in FIG. 36, and gradient-index devices, as shown in FIG. 37, may be employed as the phase modulators 5 and 6.

Additionally, as the phase modulators 5 and 6, a fly-eye lens or a microlens array, in which numerous minute lenses are arrayed, or a microprism array, in which numerous minute prisms are arrayed, may be employed.

In addition, in the case in which the image-forming optical systems 1 according to the above-described embodiments are applied to endoscopes, as shown in FIG. 38, a phase disturbing device 5 needs to be disposed inside the objective lens (image-forming lens) 70, and the wavefront restoring device 6 needs to be disposed in the vicinity of an ocular lens 73 that is positioned on the opposite side from the objective lens 70 with a relay optical system 72 that includes a plurality of field lenses 4 and focusing lenses 71 placed therebetween. By doing so, it is possible to make intermediate images formed in the vicinity of the surfaces of the field lenses 4 unsharp, and it is possible to make the final image formed by the ocular lens 73 sharp.

In addition, as shown in FIG. 39, the wavefront disturbing device 5 may be provided in an endoscope-type small-diameter objective lens 74 including an inner focusing function, in which a lens 61 a is driven by an actuator 62, and the wavefront restoring device 6 may be disposed in the vicinity of the pupil position of a tube lens (image-forming lens) 76 provided in a microscope main unit 75. As in this configuration, although the actuator itself may be a known lens driving means (for example, a piezoelectric element), it is important that the arrangement allows spatial modulation of the intermediate image from the standpoint of moving the intermediate image on the Z axis, similarly to the above-described embodiments.

In the above-described embodiments, the case where unsharpening of an intermediate image by spatial modulation is applied to the image-forming optical system of an observation apparatus has been discussed, from the standpoint of moving the intermediate image on the Z axis. Similarly, this may also be applied to an observation apparatus, from the standpoint of moving the intermediate image on the XY axis (or XY plane), which is another standpoint.

The above-discussed phase modulators for the image-forming optical system of the present invention may have an aspect described below, and a person skilled in the art could consider the most appropriate embodiment, on the basis of the idea described below. According to the following aspect, because phase modulators for an image-forming optical system characterized by having a configuration for adjusting or increasing spatial disturbance and canceling out of the disturbance applied by the above-described (a pair of) phase modulators, it may be said that it is possible to develop the unique advantageous effect provided by the phase modulators of the present invention or to make it advantageous in practical use.

(1) Periodical recess-and-projection structure type phase modulator

For example, an image-forming optical system may be characterized in that the first phase modulator for unsharpening and the second phase modulator for recovery have such a shape that the modulation distribution in a region where the phase is advanced with respect to the average value of the phase-modulation distribution and the modulation distribution in a region where the phase is delayed with respect to the average value are symmetrical with respect to the average value, and in that a plurality of pairs of the phase-advancing region and the phase-delaying region are formed periodically. By using two phase modulators having the same shape and by appropriately arranging them in an optical system in this way, complementary phase modulations can be performed, that is, an intermediate image can be unsharpened with the first phase modulator and the final image can be sharpened with the second phase modulator, and hence, the intermediate-image problem can be solved. Herein, there is no need to prepare two different types of phase modulator, and only one type is sufficient. Hence, it is possible to manufacture the apparatus easily and to reduce the cost.

Furthermore, the first and the second phase modulators may perform phase modulation by means of the surface shape of an optical medium (for example, a shape in which shapes each composed of a recessed portion and a projecting portion are periodically arranged). This makes it possible to produce the necessary phase modulators by the same manufacturing method as typical phase filters. Furthermore, the first and the second phase modulators may perform phase modulation by means of the interface shapes of a plurality of optical media. This enables more precise phase modulation than those having the same optical medium shape accuracy. Alternatively, the phase modulators can be produced with lower optical-medium shape accuracy, in other words, at a lower cost, than those having the same phase modulation accuracy. Furthermore, the first and the second phase modulators may have one-dimensional phase distribution characteristics. This makes it possible to effectively unsharpen an intermediate image. Furthermore, the first and the second phase modulators may have two-dimensional phase distribution characteristics. This makes it possible to effectively unsharpen an intermediate image.

Although the respective embodiments of the present invention have been described in detail above with reference to the drawings, the specific configurations are not limited to those in the embodiments, and design changes and the like that do not depart from the scope of the present invention are also included. For example, the present invention may be applied not only to the above-described respective embodiments and the modifications thereof, but also to embodiments in which the above-described embodiments and the modifications thereof are appropriately combined; it is not specifically limited.

As a result, the above-described embodiments lead to the following aspects.

A first aspect of the present invention is an image-forming optical system including: a plurality of image-forming lenses that form a final image and at least one intermediate image; and a first phase modulator and a second phase modulator that are disposed at positions having any of the intermediate images formed by the plurality of image-forming lenses therebetween and that apply phase modulation to the wavefront of light coming from an object. The first phase modulator and the second phase modulator have the same phase distribution including a wave-shaped phase-advancing region and phase-delaying region that are symmetrical to each other, and are paired such that light passes through the corresponding phase-advancing region and phase-delaying region having opposite wave shapes.

According to this aspect, the light entering from the object side is focused by the image-forming lenses and forms the intermediate image and the final image. Furthermore, as a result of the light passes through the corresponding phase-advancing region and phase-delaying region having opposite wave shapes, in the first phase modulator and the second phase modulator, complementary phase modulations are applied to the wavefront. Hence, as a result of the light passing through the first phase modulator, which is disposed on the object side of one of the intermediate images, spatial disturbance is applied to the wavefront of the light, and a blurred intermediate image is formed, and, as a result of the light after forming the intermediate image passing through the second phase modulator, the spatial disturbance of the wavefront applied by the first phase modulator is canceled out, and a sharp final image is formed.

By blurring the intermediate image in this way, it is possible to prevent a disadvantage in that any flaw, foreign matter, defect, or the like existing on the surface of or inside an optical element overlaps the intermediate image and eventually forms a part of the final image, even when this optical element is disposed at the position of the intermediate image.

In this case, by using the first phase modulator and the second phase modulator having the same phase distribution, it is possible to simplify the manufacturing process and to reduce the cost, compared with a case where two types of phase modulators having different phase-modulation distributions have to be prepared.

In the above aspect, the first phase modulator and the second phase modulator may each include a plurality of pairs of the phase-advancing region and the phase-delaying region that are arranged periodically.

With this configuration, it is possible to more complexly unsharpen the intermediate image, as the number of the plurality of pairs of the phase-advancing region and the phase-delaying region through which light passes increases.

In the above aspect, the first phase modulator and the second phase modulator may apply phase modulation to the wavefront by means of the surface shape of the optical medium.

With this configuration, it is possible to apply phase modulation corresponding to the recess-and-projection shape on the surface to the wavefront of the light, when the light passes through the first phase modulator and the second phase modulator. Such phase modulators can be produced by the same manufacturing method as typical phase filters, and thus, it is possible to further simplify the manufacturing process and reduce the cost. The optical medium may be either, for example, a material having a uniform refractive index or a material having a symmetrically varying refractive index.

In the above aspect, the first phase modulator and the second phase modulator may apply phase modulation to the wavefront by means of the interface shapes of a plurality of optical media.

With this configuration, it is possible to apply more precise phase modulation to the wavefront of light than that in the case where a single optical medium having the same shape accuracy is used. Furthermore, because the shape accuracy of the optical media required to achieve the same phase-modulation precision is lower than that in the case where a single optical medium is used, it is possible to manufacture the phase modulators at even lower cost.

In the above aspect, the first phase modulator and the second phase modulator may have one-dimensional phase distribution characteristics.

With this configuration, it is possible to effectively unsharpen the intermediate image.

In the above aspect, the first phase modulator and the second phase modulator may have two-dimensional phase distribution characteristics.

With this configuration, it is possible to more complexly unsharpen the intermediate image than in the case where the first phase modulator and the second phase modulator having one-dimensional phase distribution characteristics are used.

A second aspect of the present invention is an illumination apparatus including: any of the above-described image-forming optical systems; and a light source that is disposed on the object side of the image-forming optical system and that generates illumination light to be made to enter the image-forming optical system.

According to this aspect, by making the illumination light emitted from the light source disposed on the object side enter the image-forming optical system, it is possible to radiate the illumination light onto an observation object disposed on the final-image side. In this case, because the intermediate image formed by the image-forming optical system is blurred by the first phase modulator, it is possible to prevent a disadvantage in that any flaw, foreign matter, a defect, or the like existing on the surface of or inside an optical element overlaps the intermediate image and eventually forms a part of the final image, even when this optical element is disposed at the position of the intermediate image.

A third aspect of the present invention is an observation apparatus including: any of the above-described image-forming optical systems; and a photo-detector that is disposed on the final-image side of the image-forming optical system and that detects light emitted from an observation object.

According to this aspect, it is possible to detect, with a photo-detector, a sharp final image formed by the image-forming optical system by preventing the image of a flaw, foreign matter, a defect, or the like on the surface of or inside an optical element from overlapping the intermediate image.

A third aspect of the present invention is an observation apparatus including: any of the above-described image-forming optical systems; a light source that is disposed on the object side of the image-forming optical system and that generates illumination light to be made to enter the image-forming optical system; and a photo-detector that is disposed on the final-image side of the image-forming optical system and that detects light emitted from an observation object.

According to this aspect, it is possible to acquire a sharp final image over an illumination-light scanning area in the observation object.

A fourth aspect of the present invention is an observation apparatus including: the above-described illumination apparatus; and a photo-detector that detects light emitted from an observation object illuminated with the illumination apparatus. The light source is a pulsed-laser light source.

According to this aspect, it is possible to perform multiphoton-excitation observation of the observation object.

An aspect of the invention, serving as a reference example of the present invention, provides phase modulators for an image-forming optical system that includes: a plurality of image-forming lenses that form a final image and at least one intermediate image; a first phase modulator that is disposed on the object side of any of the intermediate images formed by the image-forming lenses and that applies spatial disturbance to the wavefront of light from the object; and a second phase modulator that is disposed at a position where at least one intermediate image is disposed between itself and the first phase modulator and that cancels out the spatial disturbance applied to the wavefront of the light from the object by the first phase modulator, and that is characterized by having a configuration for adjusting or increasing the spatial disturbance and the canceling of the disturbance applied by the phase modulators.

In this specification, two concepts about the form of an image, namely, “sharp image” and “unsharp image” (or “unfocused image”) are used.

First, a “sharp image” is an image that is generated via an image-forming lens in a state in which a spatial disturbance is not applied to the wavefront of the light emitted from the object or in a state in which a disturbance that is applied once is cancelled out and eliminated, and refers to an image having a spatial frequency band determined by the wavelength of the light and the numerical aperture of the image-forming lens, a spatial frequency band based thereon, or a desired spatial frequency band in accordance with the purpose.

Next, an “unsharp image” (or an “unfocused image”) is an image that is generated via an image-forming lens in a state in which a spatial disturbance is applied to the wavefront of the light emitted from the object, and refers to an image having properties such that a final image is formed so as to include practically no blemishes, foreign objects, defects or the like that exist on a surface of or inside an optical element disposed in the vicinity of that image.

An “unsharp image” (or an “unfocused image”) formed in this way differs from a simple out-of-focus image in that, including an image at a position at which the image was originally supposed to be formed (that is, a position at which the image would be formed if the spatial disturbance were not applied to the wavefront), an unsharp image does not have a clear peak of the image contrast over a large area in the optical-axis direction and that the spatial frequency band thereof is always narrower as compared with the spatial frequency band of a “sharp image”.

The “sharp image” and the “unsharp image” (or the “unfocused image”) in the present specification are based on the above-described concepts, and, in the present invention, moving the intermediate image on the Z axis means to move the intermediate image in a unfocused state. Furthermore, Z-axis scanning is not limited solely to the movement of light on the Z axis, but may involve the movement of light on the X and Y, as described below.

With this aspect, the light that has entered the image-forming lenses from the object side is focused by the image-forming lenses, thus forming the final image. In this case, by passing through the first phase modulator, which is disposed closer to the object than one of the intermediate images, a spatial disturbance is applied to the wavefront of the light, and thus, the intermediate image that is formed is made unclear. In addition, the light that has formed the intermediate image passes through the second phase modulator, and thus, the spatial disturbance applied to the wavefront thereof by the first phase modulator is cancelled out. By doing so, in the final-image formation, which is performed after the light passes through the second phase modulator, it is possible to acquire a sharp image. In particular, because of a scanning system, in the light passing through the image-forming optical system, the intermediate image moves on the Z axis while maintaining the above-described spatially modulated state, and thus, during the Z-axis scanning, the intermediate image in a blurred state passes through all the lenses in the image-forming optical system.

Specifically, by making the intermediate image unclear, even if some optical element is disposed at the intermediate-image position, and blemishes, foreign objects, defects, or the like exist on the surface of or inside this optical element, it is possible to prevent the occurrence of a problem whereby the blemishes, foreign objects, defects, or the like are superimposed on the intermediate image and are included as part of the finally formed final image. Furthermore, when the present invention is applied to a microscope optical system, even if the intermediate image moving on the Z axis by focusing or the like overlaps a lens located in front of or behind it, a noise image, in which a flaw or foreign matter on the surface of the lens or a defect or the like inside the lens appears in the final image, does not occur.

In the above-described aspect, the first phase modulator and the second phase modulator may be disposed in a vicinity of pupil positions of the image-forming lenses.

By doing so, the sizes of the first phase modulator and the second phase modulator can be reduced by disposing them in the vicinity of the pupil positions where beams do not change.

In addition, the above-described aspect may be provided with an optical-path-length varying part that can vary an optical-path length between the two image-forming lenses disposed at positions that sandwich any one of the intermediate images.

By doing so, by changing the optical-path length between the two image-forming lenses by actuating the optical-path-length varying means, it is possible to easily change the image-forming position of the final image in the optical-axis direction.

In addition, in the above-described aspect, the optical-path-length varying part may be provided with a flat mirror that is disposed perpendicularly to an optical axis and that reflects light that forms the intermediate images so as to fold back the light; an actuator that moves the flat mirror in an optical-axis direction; and a beam splitter that splits the light reflected by the flat mirror into light in two directions.

By doing so, the light coming from the object side, which is collected by the object-side image-forming lens, is reflected by the flat mirror to be folded back and is subsequently split by the beam splitter, thus being made to enter the image-side image-forming lens. In this case, by moving the flat mirror in the optical-axis direction by actuating the actuator, it is possible to easily change the optical-path length between the two image-forming lenses, and thus, it is possible to easily change the image-forming position of the final image in the optical-axis direction.

In addition, the above-described aspect may be provided with a variable spatial phase modulator that is disposed in a vicinity of a pupil position of any one of the image-forming lenses, and that changes a position of the final image in the optical-axis direction by changing a spatial phase modulation to be applied to the wavefront of the light.

By doing so, it is possible to apply a spatial phase modulation to the wavefront of the light such that the final-image position is changed in the optical-axis direction by means of the variable spatial phase modulator, and it is possible to easily change the image-forming position of the final image in the optical-axis direction by adjusting the phase modulation to be applied.

In addition, in the above-described aspect, a function of at least one of the first phase modulator and the second phase modulator may be performed by the variable spatial phase modulator.

By doing so, it is possible to make the variable spatial phase modulator bear the function of applying a spatial phase modulation that changes the final-image position in the optical-axis direction and a phase modulation that makes the intermediate image unclear or a phase modulation that cancels out the unclearness of the intermediate image. By doing so, it is possible to form an image-forming optical system with a simple configuration by reducing the number of components.

In addition, in the above-described aspect, the first phase modulator and the second phase modulator may apply, to a wavefront of a beam, phase modulations that change in a one-dimensional direction perpendicular to an optical axis.

By doing so, it is possible to make the intermediate image unclear by applying, to the wavefront of the light, the phase modulation that changes in a one-dimensional direction perpendicular to the optical axis by using the first phase modulator, and, even if some optical element is disposed at the intermediate-image position and blemishes, foreign objects, defects, or the like exist on the surface of or inside this optical element, it is possible to prevent the occurrence of a problem whereby the blemishes, foreign objects, defects, or the like are superimposed on the intermediate image and are included as part of the finally formed final image. In addition, it is possible to form a sharp final image without blurriness by applying, to the wavefront of the light, the phase modulation that cancels out the phase modulation that has changed in the one-dimensional direction by using the second phase modulator.

In addition, in the above-described aspect, the first phase modulator and the second phase modulator may apply, to a wavefront of a beam, phase modulations that change in two-dimensional directions perpendicular to an optical axis.

By doing so, it is possible to more reliably make the intermediate image unclear by applying, to the wavefront of the light, the phase modulation that changes in the two-dimensional directions perpendicular to the optical axis by using the first phase modulator. In addition, it is possible to form a sharper final image by applying, to the wavefront of the light, the phase modulation that cancels out the phase modulation that has changed in the two-dimensional directions by using the second phase modulator.

In addition, in the above-described aspect, the first phase modulator and the second phase modulator may be transmitting-type devices that apply phase modulations to a wavefront of light when allowing the light to pass therethrough.

In addition, in the above-described aspect, the first phase modulator and the second phase modulator may be reflecting-type devices that apply phase modulations to a wavefront of light when reflecting the light.

In addition, in the above-described aspect, the first phase modulator and the second phase modulator may have complementary shapes.

By doing so, it is possible to employ simple configurations in the first phase modulator that applies, to the wavefront, the spatial disturbance that makes the intermediate image unclear and the second phase modulator that applies the phase modulation that cancels out the spatial disturbance applied to the wavefront.

In addition, in the above-described aspect, the first phase modulator and the second phase modulator may apply phase modulations to a wavefront by using a refractive-index distribution of a transparent material.

By doing so, it is possible to generate a wavefront disturbance in accordance with the refractive-index distribution when the light passes through the first phase modulator, and it is possible to apply, to the wavefront of the light, the phase modulation that cancels out the wavefront disturbance by using the refractive-index distribution when the light passes through the second phase modulator.

In addition, another aspect of the invention, serving as a reference example of the present invention, provides an illumination apparatus including any one of the above-described image-forming optical systems and a light source that is disposed on an object side of the image-forming optical system and that generates illumination light to be made to enter the image-forming optical system.

With this aspect, by making the illumination light emitted from the light source disposed on the object side enter the image-forming optical system, the object to be illuminated, disposed on the final-image side, can be illuminated by the illumination light. In this case, because the intermediate image formed by the image-forming optical system is made unclear by the first phase modulator, even if some optical element is disposed at the intermediate-image position and blemishes, foreign objects, defects, or the like exist on the surface of or inside this optical element, it is possible to prevent the occurrence of a problem whereby the blemishes, foreign objects, defects, or the like are superimposed on the intermediate image and are included as part of the finally formed final image.

In addition, another aspect of the invention, serving as a reference example of the present invention, provides an observation apparatus including any one of the above-described image-forming optical systems and a photo-detector that is disposed on a final-image side of the image-forming optical system and that detects light emitted from an observation subject.

With this aspect, with the photo-detector, it is possible to detect a sharp final image that is formed by preventing images of blemishes, foreign objects, defects, or the like on the surface of or inside the optical element from being superimposed on the intermediate image by using the image-forming optical system.

In the above-described aspect, the photo-detector may be disposed at a final-image position in the image-forming optical system and is an image-acquisition device that captures the final image.

By doing so, it is possible to perform high-precision observation by capturing a sharp final image by using the image-acquisition device disposed at the final-image position in the image-forming optical system.

In addition, another aspect of the invention, serving as a reference example of the present invention, provides an observation apparatus including any one of the above-described image-forming optical systems; a light source that is disposed on an object side of the image-forming optical system and that generates illumination light to be made to enter the image-forming optical system; and a photo-detector that is disposed on a final-image side of the image-forming optical system and that detects light emitted from an observation subject.

With this aspect, the light coming from the light source is focused by the image-forming optical system and is radiated onto the observation subject, and the light generated at the observation subject is detected by the photo-detector that is disposed on the final-image side. By doing so, it is possible to detect a sharp final image with the photo-detector, which is formed by preventing images of blemishes, foreign objects, defects, or the like on the surface of or inside the intermediate optical element from being superimposed on the intermediate image.

The above-described aspect may be provided with a Nipkow-disk-type confocal optical system that is disposed between the light source, and the photo-detector and image-forming optical system.

By doing so, it is possible to acquire a sharp image of the observation subject at high speed by scanning the observation subject with multiple spots of light.

In addition, in the above-described aspect, the light source may be a laser light source, and the photo-detector may be provided with a confocal pinhole and a photoelectric conversion device.

By doing so, it is possible to observe the observation subject by using a sharp confocal image in which images of blemishes, foreign objects, defects, or the like at the intermediate-image position do not appear.

In addition, another aspect of the invention, serving as a reference example of the present invention provides an observation apparatus including the above-described illumination apparatus and a photo-detector that detects light emitted from an observation subject that is illuminated by the illumination apparatus, wherein the light source is a pulsed laser light source.

By doing so, it is possible to observe the observation subject by using a sharp multi-photon-excitation image in which images of blemishes, foreign objects, defects, or the like at the intermediate-image position do not appear.

The present invention affords an advantage in that the manufacturing process is simple, the cost is low, and it is possible to acquire a sharp final image by preventing blemishes, foreign objects, defects, or the like in an optical element from being superimposed on an intermediate image even if the intermediate image is formed at a position coinciding with the optical element. Moreover, by improving the phase modulators, it is possible to acquire an even sharper final image.

REFERENCE SIGNS LIST

-   I final image -   II intermediate image -   O object -   PP_(O), PP_(I) pupil position -   1, 13, 32, 42 image-forming optical system -   2, 3 image-forming lens -   5, 5′ wavefront disturbing device (first phase modulator) -   6, 6′ wavefront restoring device (second phase modulator) -   10, 30, 40, 50, 60 observation apparatus -   11, 31, 41 light source -   14, 33 image-acquisition device (photo-detector) -   17 phase modulator (wavefront disturbing device, first phase     modulator) -   23 phase modulator (wavefront restoring device, second phase     modulator) -   20, 36 beam splitter -   22 optical-path-length varying means -   22 a flat mirror -   22 b actuator -   28, 38 illumination apparatus -   34 Nipkow-disk-type confocal optical system -   43 confocal pinhole -   44 photo-detector (photoelectric conversion device) -   61 a lens (optical-path-length varying means) -   62 actuator (optical-path-length varying means) -   64 spatial light modulator (variable spatial phase modulator) 

1. An image-forming optical system comprising: a plurality of image-forming lenses that form a final image and at least one intermediate image; and a first phase modulator and a second phase modulator that are disposed at positions having any of the intermediate images formed by the plurality of image-forming lenses therebetween and that apply phase modulation to the wavefront of light coming from an object, wherein the first phase modulator and the second phase modulator have the same phase distribution including a wave-shaped phase-advancing region and phase-delaying region that are symmetrical to each other, and are paired such that light passes through the corresponding phase-advancing region and phase-delaying region having opposite wave shapes.
 2. The image-forming optical system according to claim 1, wherein the first phase modulator and the second phase modulator each include a plurality of pairs of the phase-advancing region and the phase-delaying region that are arranged periodically.
 3. The image-forming optical system according to claim 1, wherein the first phase modulator and the second phase modulator apply phase modulation to the wavefront by means of the surface shape of the optical medium.
 4. The image-forming optical system according to claim 1, wherein the first phase modulator and the second phase modulator apply phase modulation to the wavefront by means of the interface shapes of a plurality of optical media.
 5. The image-forming optical system according to claim 1, wherein the first phase modulator and the second phase modulator have one-dimensional phase distribution characteristics.
 6. The image-forming optical system according to claim 1, wherein the first phase modulator and the second phase modulator have two-dimensional phase distribution characteristics.
 7. An illumination apparatus comprising: the image-forming optical system according to claim 1; and a light source that is disposed on the object side of the image-forming optical system and that generates illumination light to be made to enter the image-forming optical system.
 8. An observation apparatus comprising: the image-forming optical system according to claim 1; and a photo-detector that is disposed on the final-image side of the image-forming optical system and that detects light emitted from an observation object.
 9. An observation apparatus comprising: the image-forming optical system according to claim 1; a light source that is disposed on the object side of the image-forming optical system and that generates illumination light to be made to enter the image-forming optical system; and a photo-detector that is disposed on the final-image side of the image-forming optical system and that detects light emitted from an observation object.
 10. An observation apparatus comprising: the illumination apparatus according to claim 7; and a photo-detector that detects light emitted from an observation object illuminated with the illumination apparatus, wherein the light source is a pulsed-laser light source. 